1. Field of the Invention
The invention relates to an electrically heated catalytic device and a vehicle, and may be applied to, for example, an exhaust gas control device provided in the exhaust system of a hybrid vehicle that includes an engine and an electric motor or another kind of vehicle, and a vehicle equipped with the exhaust gas control device.
2. Description of Related Art
A metal catalyst (platinum, palladium, or the like) used in the purification of exhaust gas, which is fitted in an exhaust system (i.e., an exhaust pipe) of an automobile exerts high catalytic activity under high-temperature conditions. Accordingly, when the exhaust system is still cold, such as when an engine is first started, the catalyst, which is fitted in the exhaust system, has lower activity than when the engine has been running continuously for a period of time. Thus, there have been demands for an art of instantaneously purifying exhaust gas even under such a circumstance. In particular, a hybrid vehicle, which has become increasingly popular recently, can not only run by being driven by an engine but also run only by an electric motor (i.e., by a power from a battery) (perform EV running). In conjunction with this EV running, the engine is frequently stopped. In a plug-in hybrid vehicle, EV running plays a more principal role. In a hybrid vehicle, the cold state of the exhaust system as during the aforementioned start of the engine may continue even after the vehicle has been moving for a while. There have been demands for an art of quickly purifying exhaust gas even under such a circumstance.
In order to meet the aforementioned demand, Japanese Patent Application Publication No. 5-115795 (JP-A-5-115795) describes an exhaust gas control device that includes an exhaust gas purification catalyst (a metal catalyst) for the purpose of improving the capacity to purify exhaust gas in a cold state as during the start of an engine. The described exhaust gas control device includes an energization-exothermic honeycomb carrier and a pair of electrodes connected to the honeycomb carrier. The exhaust gas control device supplies power to the electrodes to energize the honeycomb carrier, thereby causes the honeycomb carrier to generate heat, which in turn heats the exhaust gas purification catalyst.
However, the conventional energization-exothermic exhaust gas control device described in JP-A-5-115795 takes no countermeasure against the influence of soot present in exhaust gas. That is, the soot present in exhaust gas is a conductive material that mainly contains carbon. Therefore, when the soot discharged from the engine accumulates on the energization-exothermic honeycomb carrier, the deposits of soot may cause short-circuiting in an unexpected region of the honeycomb carrier. Such unforeseen short-circuiting leads to a failure in the generation of heat from the honeycomb carrier or causes inconveniences such as electrical leakage and the like through the formation of an unexpected conductive path in the exhaust gas control device, and is therefore unfavorable.